Insulating material



April 24, 19,51 F. T. GoRsKl INSULATING MATERIAL Filed July 29, 1948 /J uw), fai, A

Patented Apr. 24, 95

v .lNSULA'llNG MATEJSHAL Florian Gorski, Granville, -0hio, assignor to Owens-i Corning Fiberglas Corporation, fa. Ycor.: ffporationiof:Delaware Arrlicationluly1948,"Serialgll9f 4;.1324

,9 claims. (01154?44) This 'invention relates mineral mfiber -produots which havevparticular application -as ther-mal insulation, Wall board,

to 'glass Yand otherrooi-ng, -sidingf-androther dik-e building materials The products -may also be usedas electrical insulationparticularly as pa-nel board. l

VvIt is an object of lthis inventionvto provide insulation andstructural material of glass Aiibers bonded into an integral body of' relatively -nxe'd dimensions' 4and Aharing greatly increased 4compressive strength, resistance -to delamination and nail-holding Vpower over products known heretofore, Vand -having lat vthe lsame iti-me s-uicient v'porosity -to enable its use -as an insulation, Wall board, siding, or other structuralmateri-al.

-Morespecically, Ait-isanobjecft to produce ra glass ber boa-rdfin -which 4the bers Aare secured one -toA another 4 attherfjunctures 'by Va relatively infusible, yrigidbinder --to 4provide a porous mat of -iixed dimension, the L-bers subseci-uemzly being coated vsubstantially throughout ltheir lengths wtha less rigid A-andniore flexible `rnaterialto impart a marked `improvement in -character-iStic-s.

A iur-ther object lis to produce a ylami-I-i-ate material such-was -bitumens,-and inner `layer-s' of a porous fabric vof Lglass'fz'loers -seeuredone lLto -another 'by an infusiblebinder and impregnated f 3Q lanother by ian iin-fusible and ypreferahly .an inf 35 bonded `one .-.to another oto form an integral.;

tion, not.4 of flimitation, embodiments Sof the i-n- A ventionarehshoiwn in theaccompanying .drawings,iin=which:

JFigure .1 is a greatly -expanded fragmentary View of a bondedglass yfiberhmathf .fthe A.type adapted for subsequent treatment in --the manner embodying the features of this invention;

Figure 2 is `a .greatly expanded-fragmentary View of a .treatedmaty embodying-.the featuresnf this.` invention;

-Figure 3` is a fragmentary'toptviewfof aproduct produced bythis invention;

.Figure 4 is aaview `,of Aa-segrnent pf roof deck insulationin the form pf a .laminateiembodying the 'featuresfofthis invention;

f4() 'rare usedrwith:glassenbersftheyftendtmmgrategto5:

the junctures .of the @bers lwhere rthey'ibecome -Eieure ...521s illustrated :110W isheet .showing theumeans foroarryng-ontfth invention; and

liglireo isfaiowssheetgofia modiedmiethod for.rarryngfutethelvinwention.

'L'The product Aofatheinvention is -eharaoteriaed by--the 'fact that \af-abric,-web,mah-or boardds first formeel of Iglass 'bers 'which are :bonded f one-'totanotherin amanner toform-an integr-a1 porous -mat -of -permanentl-y fixed dimensions.

Thereafter, the fibers of "the lporous 'mat .are

coated substantial-ly ithroiug-hout their Ylengths with `a compound capable of 4imparting cert-ain: desirablel characteristics-to`-the mat. Ffhisooatv 'l0 ing may be achievedbyiimpregnation of=the\mat ...and the impregnation wmay be regulated to 1insulation applications. 'Ehe-ratio of yimpregnant to mat, onA the other `lhand,y mayrunas high asew or #20 fparts to-vone on the vweightbasis-.iin which 20 case a dense and Ncompact --product is producedfhaving few#voidsand-marioehighenougn-Where f desired-to prot/'ideah produet-wthattissubstantialltr void-free, -the Jresulting products vhavingiolnavraoteristicsdesirable-orlstructural boardsandinhaving continuous spa-ced \1layers `of resin-like l25 sulations.ofogreatrstrengthfand iwhiohiwill hold .i

nails, :screwsroriothen fastening members.

In forder to xsecureqoe1-Ii1f.a,nenc,eewitl'iirespectJto the rfiber arrangement vinte-the -produ-ct :and :oor:

respondingly xed and ..fpermanentfdimensions i solublefor -.relati=vely inert resin. l'-n rBergin and SimisomRatentfNo. 225231157.;thereiscdescrbedia suitable `process foriproducing mats. of `tide-:types described 4Avi/'herein la mass `fof .glass bers lare porous .product-.by ...a ithermosetting resin fof ith@ types ;,of phenol .formaldehyde or urea@formale dehyde .in .fcombination iwith .fan .immiscible oil.

When smalLamountsofesuch:bindertcompositions set .and V.as .La .result aine :desired permanence of ber arrangement .is .secured with a .minimum amountioffresinous binder,

nished mat; has' beenffoundstmhe suicient, .ibut

when .it @is L.desired to secure :the fbers ftogether miao-high. density Amassfof :sayA gto flot-pounds per icubicfoot, `oinclina-rile?,ffl to :151% :or more ybinder hisLinViention, instead is used. :In carrying4out ofisecurinezithegglass fillers' Y immseible fnleaeinoiisvpheno. C i ble.;boriosrnaygbeseeuredwith a at,.

Whenoa relativelyfluffy-*fabric is desired, as little as 1% binder on theebass:ofmeightoftthe Y hardexfablef @phenolic salone.. @Set renditions may :hett

secured by other resinous materials capable of reaction to a stage wherein they are not softened by elevated temperatures to such an extent as to flow when impregnation is effected from a hot melt, are relatively resistant to solvents to which the mat may be subjected during the impregnating process, and have no cold flow.

Illustrative of other suitable ber bonding materials for use with or without oleaginous or other hydrocarbon admixtures are the reaction products of an aldehyde such as formaldehyde, furfuraldehyde and the like with cresol, resorcinol, analine and the like, or With urea, melamine or other nitrogenous resin-forming derivatives. Use may be made of the polyesters such as the reaction products of polycarboxylic acids with polyhydric alcohols having sufficient functional groups or unsaturated groups capable of such linkages as will form an infusible product, and 'copolymers of the polyesters with vinyl derivative monomers such as styrene, vinyl chloride, vinyl acetate, acrylates andthe like. I may also use the allylic polymers and copolymers thereof with polyesters and vinyl derivatives of the type described above.

The reaction products of furfural and furfuryl alcohol separately or in admixture with or Without catalysts have also been used in the fabricationof mats of xed dimension.

The desired characteristics of permanence in dimension may also be secured where more flexible and resilient binders are used, enabling a product of greater flexibility, softness, and resiliency to be produced. The principal ingredient in the binder is still cross-linked or of suiciently high molecular weight to resist flow under impregnating conditions but is constituted of exibilizing long chain groups or is modified or plasticized with exibilizing ingredients. For example, a resilient or flexible binder may comprise -an A stage phenolic resin in admixture or solution with an oil or a rubber compostion ofthe type Buna-N which includes various ratios of acrylonitriles copolymerized with butadiene. YIt may comprise a phenolic resin extended With natural resins, asphalts, or Vinsol, which latter is the product ofthe steam distillation process of pine Wood.

.In the main, these resinous binders are relatively brittle in their .,curedstage with the re.- sult that the binder or fibers or both appear to crack or Vbreak under pressure or compression. This characteristic becomes more pronounced as thebinder concentration in the mat is increased and a bat of interbonded fibers is handicapped for many applications for which it might other- Wise be employed. Greater Ilexibility is secured with a reduction of binder concentration, but accompanied with such reduction is a loss of vpermanence of dimensions with the consequence that aboard-like product cannot be produced.

I have found that exceptional properties are secured- When the mat of interbonded glass bers is subsequently treated with materials having less rigidity and/or less resistance to deformation than the basic binder.

I have found further that by the after-treatment of the bonded fabric with impregnants which, incidentally may be low cost materials, to coat the bonded bers substantially throughout their lengths and partially to lill the interstices between the fibers in the fabric, there is produced a porous light-weight mineral liber insulation product lhaving greatly improved strength, especially compressive strength. The

4 nal product is still highly porous, which insures good insulating characteristics. The impregnated structure is much more resistant to delamination and has greatly improved nail-holding power than mineral fiber products heretofore known.

By controlling the density of the fibrous mass and the amount of impregnant, products having a density of several pounds per cubic foot up to as much as pounds per cubic foot may be produced. Depending on the characteristics of the specific impregnant used, the product may have the characteristics of a resilient board or it may simulate a structure of marked hardness but even in the latter instance the product may be still sulciently porous to have substantial insulating properties.

By the use of the subsequently applied impregnating compositions, the desired mass integrity of the product can be secured with the use of less of the initially applied and more expensive binder. By impregnation of the mat and coating of the iibers only through selected crosssections of the mat, further economies can be effected While still obtaining, though in reduced measure, the desired properties in the nal product. Impregnation in a manner to coat the bers substantially throughout theirrlengths is eliective to protect the fibers one from another to resist ber disintegration by reason of abrasion during flexure of the mat, and tov eliminate fly, or sifting out of broken fibers, as well as brashiness during flexure, compression or other fiber or mat deformation.

The desired characteristics are secured when the impregnant is a composition which, when set, has one or more of the properties of less rigidity and greater yieldability or exibility than the v binder securing the fibers together in the mat.

Novel and improved characteristics are also secured when the impregnant is of the same general characteristic as the binder but preferably extended with less costly or modifying materials to reduce the ultimate cost of the product as well as to impartvtailor-made characteristics.

Suitable impregnating compositions may be selected of materials such as bitumens, natural resins, synthetic resins, rubber-like materials and the like, and mixtures thereof.

The term bitumens is meant to include the various asphaltics which may be grouped to include mineral waxes, native asphalts, and asphaltic bitumens; tars and pitches of the type v wood tar, wood tar pitch, coal tar, coal tar pitch,

fatty acid pitches and the like; asphalts and waxes such as paramn wax, petroleum wax, wax tailings and resins, and petroleum resins.

vNatural resins include such materials as rosin, rosinates, and rosin derivatives; Vinsol (a product of the steam distillation of pine wood) gums,

copal, dammar, lignin, and shellac.

Suitable synthetic resinous materials for impregnation preferably are selected of the thermoplastics which include the cellulosic ethers and esters of the type nitrocellulose, ethylcellulose or other alkyl cellulose compositions, celluose acetate, cellulose butyrate and the like; polyalkyl acrylates represented by methyl methacrylate, butyl methacrylate and methylbutyl acrylate; polystyrene, polyethylene, pclybutene, polyamides, coumarone-indene resins, polyterpene hydrocarbon resins, and polyvinyl compounds of the type polyvinyl chloride, polyvinyl acetate, polyvinyl acetals, copolymers of polyvinyl chloride and polyvinyl acetate and copolymers 1of.polyvinylidene chloride withrotherocom.- patible vinyl compounds. f

When a dense andtextremely hard board is desired, I have been able to 4impregnate mat initially bonded *with hard thermesetting `"resins of the type previouslydescribedwith like thermosetting compositions. However, inthisfinstance it is preferable to extend -thevresinous binder with compatible low cost Vplasticizing materials, such as compatible oils, `liquid "plasticizing resins, bitumens, petroleum resins and the like.

Suitable rubber-like compositions 'capable `of producing aresilient:cushionflike product, especially when more. ilexiblerbindersare::employedgas the mat binder are represented by the synthetic rubbers including Buna-N (the copolymer of acrylonitrile with butadiene), =BunaS :(-the copolymer of butadiene `.with f-styrene), `(':lfiloroprene polymers, organic polysulfides,"chlorinated rubber andthe like.

Impregnating compositionsI may comprise the above materials when used alone or one or more of the materials -in admixture with Vothers whether they be inthe same :class or of other classes of the type described. For instance, the impregnant may be a bitumen or it may be a bituminous `substance in'L admixture with a phe nolic or a polystyrene resin.

Referring to the drawing, `aporous mat I0 of glass fibers Il rsecured at their junctures with a relatively non-flowable and rigid binder I2 'is treated with impregnant 'in a manner `to ,coatthe bers substantially throughout their' lengths and partially to ll the voids or the interstices between the bers with impregnant material |13. Theimpregnant ordinarilyis applied inliquid form and is adapted to :be hardenedor-setat temperatures of use to produce-an insulation, Wall board, siding, and the like. l

The bonded mat may be preparedv by theproeess of the-Bergin and Sirnison Patent No..2 `;252, 157 wherein the phenolic binder is applied to the bers as they are rained 'down from above and collected on a supporting screen vwhicghzmavcomprise an endless belt I4, theitibers being collected .a

thereon in a somewhat felted haphazard arrangement. By controlling 'the ra'te of "fiber deposition and the linear fmovement of the belt I4, the thickness of the brous deposit canbe controlled from that of a relatively thin matof about 1/8 to 1/4 inch to a bat of several inches thickness. The binder, which maybea solution or dispersion of uncuredphenolic, urea or the like cross-polymerizible resinwi'th or Without incompatible oleaginous materials, -may be .applied-as the bers are collected on the belt i4; orxelseit may be after-applied by flow coating, :'Spraying, dipping or other suitable means. To produce `a formed mat of fixed dimension, the bat iscompressedwh'ile4 the binder is advanced tosetconditions under the influence of heat, catalyst or other activating systems. The product is a rather endless web I5 of i'lxed dimension which may be run in continuous fiashion through=-the successive steps embodied in this invention.V

Referring now to Figure 5, the Abonded Web'izB may-be. led directly from the treating oven;` Mito a-sander Il. The impregnantmaterial l3'stored in a reservoir i9 is forced by a pump I `.tato spray guns I iil for delivery onto the web. When-'the impregnant is a thermoplasticsuch asa bitumen, petroleum resin, vwaxy 4material .or ,f-a synthetic thermoplastic of the type ethyl cellulose, itmay be .applied from-solution or emulsion yor alter! natively thereservoir fmay be heatedzandgthe im- :1751;

6 pregnant may bezappliedfasaa hot-melt. When the impre'gnant ia :material incapable of iluid now-.responsive Lto elevateditemperatures, or else when it contains-immaterial of .the heat curable type .which :issensitive to` elevated temperatures, the limpregnantmay beapplied asa solution or dispersionin suitable diluents, such as solvents orwater.

.The underside of 4the web-Min thefregion-of impregnationis suiilciently conned bya cham.- berZlto -enable a--suction pumpiZ I itoy create-subatmospheric .conditions Which are effective to draw fafcalculated #portion of the impregnant through the web, thereby vtoinsure uniformfimpregnant distribution as-well as to "regulate, -to some-extent,'theamount ofimpregnant whiclrremains in the web. 'Thedrip-or withdrawn Iirnpregnant, indicated by larrows 122, is collected in the chamber and returned Aby Ya :pump y:23a

:throughpassages 523 to the 'reservoir 5I 9.

'-.Ins'tea'd of spraying the impregnating material ontofthe-sur'f-ace ofthe web, a flow proces'smay be employed incombination 'with the vacuum means to effect the desired impregnant penetration and distribution. The -bersonthe underside-1.0i .the y.web :maybe positivelycoated by 'a rollerfzllooperating in'a-bath vfed byfa conduit l2l5*fromfthelreservoir 5119.

Ordinarily lthe entire impregnating area fand an additional --zone ,21a -is enclosed to form a chamber 2.? Lwhich is heatedS-byburners 2,8 rtofa temperature -.sufcient yto lmaintain the impregnatingzm'aterials atfiiuidrcondition-so that excess impregnant may. lie-.permitted to drain from the web. For example, iwhen .asphaltic materials or petrolerunresins,:onmixtures ,thereof are used, temperatures. in the vrange .of `about.250 ,to 300 F. are sumcientforpthelower melting .point tarsand pitches, while temperatures in excess of therange of.-^B50F.,-may .be required .for ,pyrobitumens,; gilsonites, `and the like. In .addition y to ,rendering thesimpregnant moregfluid, theheat'- applied from the-burners ,Zmay operate to drive oi `diluents orto advance the cure of,resinous materialsiwhen such materialsare incorporated :asa part of the impnegnant.

eIt willebesignificant that 4during impregnation andiheating as ;described,z'the'relative positions oftthefbers in vthe vweb will remain substantially the-same-so thatthe web will hold. its xed dimension :because the binder I 2 securing the fibers together at their; junctures isof :the type which-.is unaiected by the heat and generallyinert .to .the solvents, diluents, onapplied in ipregnatingr :materials. The substancethat drains from the :batin the heating zone 2l maybe collected by the pans 29Htobe returned .forfreuse4 to the reservoir 19.

,By regulating the amount of impregnation-and the,solids in the impregnating composition, and

4bycontrolling the temperatures inthe heating zone,` the concentration of impregnant that,remains in the webmay be selectively predeter mined. Thus it'may be varied from a condition wherein ,the impregnant merely coats the bers as illustrated in Figure 2 to. produce a Very Porous insulation, or it may be so controlled thatthe greater portion of Athe'impregnant remains "in the web to yproduce arelatively dense product in which the ratio of impregnant to bonded A:bers mayrun as high as 10 -or even 20 parts to one.

the heated chamber 2l, the impregnated web -isxled by the. belt .l fifthrougha refrigerating zonel30 `where the impregnant is cooled to--set conditions as by 'passing the 4refrigerated Aair throug-hathe` pores of. the fiweb. Then inecontinu- 7 ous fashion, it is sectioned into boards or mats for use or for packaging for shipment to distant stations, such sectioning means may comprise an element such as the guillotine 3|.

In a modied system, shown in Figure 6 of the drawing, pieces 4l) of the molded and bonded porous web I5 are stacked behind a wall 4l and they are displaced individually from the bottom of the stack by cleats i2 secured cross-Wise to an endless belt 153. The displaced pieces are advanced to an impregnating bath 44 having the desired impregnant i5 in fluid form at a level suficient completely to immerse the pieces 40 as they are passed under rollers 46. During immersion, the pores of the bonded fibrous material become filled with the liquid impregnant Whereon the pieces fall to the bottom of the impregnatingl tank 44 as they are advanced by the oncoming pieces fed by the belt.

From the tank lill, the impregnated pieces pass into and through a heated area 4l for reaction as previously described in connection with the heated zone 2 of Figure 5. Here the impregnant materials are rendered sufciently fluid to drain excesses thereof from the bat and the heat operates additionally to remove volatiles When used or to advance heat-hardenable ingredients when forming a part of the impregnating composition. lIhe drip is collected on pans 58 and stored in suitable containers for reuse. These pieces of impregnated material may be advanced through the heating zone by the oncoming pieces or they may be positively carried through the Zone by a belt 69 as shown. After the pieces have been subjected to the desired amount of heating, they are advanced through a refrigerating Zone 50 to set the impregnant, and in which zone they may be separately conveyed by carriers 5l secured to an endless belt 52.

Other means employing the same general principles described, may be employed to effect the desired impregnation. For example, the impregnant in fluid' form may be forced by one or more pressure guns (not shown) through the web. In-

this connection it is possible to impregnate the web only in localized, spaced-apart areas, and similarly to the previously described form of the invention these impregnated sections provide connection between the opposite faces of the web by the more resilient impregnant to impart some of the described properties, especially resistance to delamination of the web and increased resistance to compression.

The impregnated porous mat l0 may be used as is for insulation, siding, or structural board. It may be further coated on one or both sides with layers 53 and 511i of resinous material or resin-like materials of the type described to produce a laminate having a core of porous fabric Ill faced with continuous layers 53 and 54 of material. For example, an insulation board bonded with a phenolic resin, impregnated with a bitumen, petroleum resins or mixtures thereof, and coated on its outer surfaces with a bituminous'layer nds extensive use as a roof deck insulation which may be used as is or may be subsequently treated after laying with the usual asphaltic coatings. Ordinarily layers 53 and 54 are comprised of materials'capable of strongly adhering to the fabric Iii either through partial penetration of the pores or through chemical welding such as fusion of compatible materials.

The following are illustrative of suitable binder compositions by which the glass fibers may be secured together in web or permanently fixed dimensions.

Example 1 30 percent phenolic A stage resin 3 percent sulphonated hydrocarbon oil 67 percent water Example 2 30 percent phenolic resin (A stage) 15 percent Vinsol 55 percent water The Vinsol may be reacted with the phenolic resin or added thereto in the above mixture.

Example 3 6 percent phenolic A stage resin 14 percent acrylonitrile-butadiene copolymer percent water f The composition is applied as an emulsion.

Example 4 l5 percent A stage phenolic resin 5 percent steam refined asphalt 80 percent Water The composition is applied as an emulsion of the asphalt in water-resin solution.

Example 5 20 percent of the reaction product of furfuryl alcohol in the presence of acids at elevated temperature 80 percent water The following formulations are illustrative of the impregnating compositions which may be applied in accordance with this invention:

Example 6 Asphalt M. P. -150 F.

Applied directly as a hot melt at -175 F.

Example 7 50 percent asphalt M. P. 13G-150 F. 50 percent petroleum resin Applied as a hot melt at -300 F.

Example 8 60 percent Vinsol resin 40 percent water Applied as a water emulsion.

Example 9 40 percent A stage phenolic resin 25 percent Vinsol 35 percent Water Applied as a water dispersion. The discrete particles of resin fuse at the subsequent heating step to form a composite mass.

Example 10 '70 percent A stage phenolic resin 30 percent water calculated amount,

quently impregnated or treated mat or board has the characteristics to impart yieldability, in-

creased strength, ber protection, density and nail-holdingpower to the initial Web, and it is adapted to impart these characteristics with a reduced concentration of the more expensive binder material securing the bers in the original porous fabric.

A cardinal feature of this invention resides in the construction of the impregnated product wherein the impregnant is applied in a manner to coat the fibers substantially throughout their lengths to protect the fibers against disintegration by abrasion and partially to fill the pores by a predetermined amount to produce a board suitable for many purposes. The board maybe further treated with continuous outer layers of suitable materials to provide a laminate adapted as roof deck insulation, siding, and the, like.

The invention also contemplatesthe methods *I by which the new and improved product is produced, employing successive steps of impregnation and such combination treatments as will drain excesses of impregnant over and above the and which subsequently causes the setting of the impregnant remaining in the web in situ on the bers to produce the final product which is relatively stable at temperatures of use.

It will be understood that numerous changes may be made in the compositions of the binder, the impregnant and in the treating steps to which the web is subjected in producing the final product without departing from the spirit of the invention, especially as dened in the following claims.

I claim:

V1. An article of manufacture comprising a mass of glass bers, an insoluble and infusible resinous material bonding the fibers at their intersections to form the fibers into an integrated porous body, and a thermoplastic resin impreghating the bonded mass of glass ibers'to coat the. bers substantially throughout their lengths.

2. An article of manufacture comprising a mass of glass bers, from 1 to 10 per cent by weight of .an insoluble and infusible resinous material binding the fibers together at their intersections into an integrated porous'body of predetermined shape, and from 1 to 20 parts by weight of a thermoplastic material to one part Vby weight of the bonded mass of glass bers impregnating the bonded mass of' glass fibers.

3. An article of manufacture as claimed in claim 2 in which the insoluble and infusible binder is a phenol formaldehyde resin advanced to a set stage of polymeric growth.

4. An article of manufacture as claimed in claim 2 inI which the binder is a compatible phenol formaldehyde butadiene acrylonitrile polymerization product advanced jointly to a cured stage.

5. An article of manufacture as claimed in claim 2 in which the infusible and insoluble resinous binder is a phenol formaldehyde-bitumen combination.

6. An article of manufacture as claimed in claim 2 in which the impregnant is a bitumen.

'7. An article of manufacture as claimed in claim 2 in which the impregnant is a thermoplastic resinous material.

8. An article of manufacture as claimed in claim 2 in which the impregnant is an elastomer.

9. An article of manufacture as claimed in claim 2 in Awhich the bonded and impregnated mass of glass bers is faced on at least one side with a continuous layer of a bituminous material.

FLORIAN T. GORSKI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS y Number Name Date 1,899,056 Powell Feb. 28, 1933 2,079,330 Chase Feb. 9, 1937 2,252,157 Bergin et al Aug. 12, 1941 2,292,118 Guhl Aug. 4, 1942 2,341,130 Unsworth Feb. 8, 1944 2,349,909 Meharg May 30, 1944 2,433,847 Jennings et al Jan. 6, 1948 FOREIGN PATENTS Number Country Date 525,556 Great Britain Aug. 30, 1940 

1. AN ARTICLE OF MANUFACTURE COMPRISING A MASS OF GLASS FIBERS, AN INSOLUBLE AND INFUSIBLE RESINOUS MATERIAL BONDING THE FIBERS AT THEIR INTERSECTIONS TO FORM THE FIBERS INTO AN INTEGRATED POROUS BODY, AND A THERMOPLASTIC RESIN IMPREGNATING THE BONDED MASS OF GLASS FIBERS TO COAT THE FIBERS SUBSTANTIALLY THROUGHOUT THEIR LENGTHS. 